1. Field of the Invention
The present invention relates to techniques for communicating signals between semiconductor dies. More specifically, the present invention relates to a method and an apparatus for equalizing signals that are communicated between semiconductor dies using capacitively coupled proximity pads or connectors.
2. Related Art
Researchers have begun to investigate new techniques for communicating between semiconductor chips. One promising technique involves integrating arrays of capacitive transmitters and receivers onto semiconductor chips to facilitate inter-chip communication. If a first chip is situated face-to-face with a second chip so that transmitter pads on the first chip are capacitively coupled with receiver pads on the second chip, it becomes possible to transmit signals directly from the first chip to the second chip, without having to route the signal through intervening signal lines within a printed circuit board.
In many proximity communication systems, transmit circuits in the first chip and receive circuits in the second chip are close to the transmitter pads and the receiver pads, respectively. Thus, the connecting signal lines in the chips are very short, and consequently have low resistance, low capacitance, and negligible inductance. As such, they do not present a significant load to either the transmit circuits or the receive circuits.
In some proximity communication systems, however, at least some of the signal lines between transmit circuits and/or receive circuits and the corresponding transmitter and/or receiver pads(s) may be relatively long. These signal lines may have appreciable resistance, capacitance, and possibly inductance. Hence, such signal lines may load down the transmit circuits and/or receive circuits, and may consequently introduce delays and signal loss in the proximity communication system. Such lossy interconnects may introduce a dominant pole in the proximity communication system's frequency response. This may cause signals at frequencies higher than this pole to be attenuated, thereby leading to degraded edge rates and lower data rates.
What is needed is a method and an apparatus to facilitate capacitive inter-chip communication without the problems listed above.